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4-2 Quantum Theory

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4-2 Quantum Theory

- Max Planck predicted accurately how the spectrum of radiation emitted by an object changes with temperature.

- Proposed that there is a fundamental restriction on the amounts of energy that an object emits or absorbs, called quantum.
- Means FIXED AMOUNTS

- Completely contradicted the idea that energy can emit or absorb in any amount.
- Related the Frequency of the radiation to the amount of energy.
- E = h
- Energy = Planck’s Constant x Frequency

- Planck’s Constant (h) = 6.6262 x 10-34 J-s (Joule x second)
- Energies absorbed or emitted by atoms are quantized, which means that their values are restricted to certain quantities. Energy is not continuous

- Imagine a car’s fundamental quantum of energy corresponds to a speed of 10 km/hr. If the car has 7 quanta of energy, it will have a speed of 70 km/hr. If the car has 9 quanta of energy, it will have a speed of 90 km/hr. This shows that a car can only move in multiples of 10 km/hr (in this case). Speeds such as 88 km/hr and 41 km/hr are impossible

- QuantizedContinuous

- Why can’t we see quantized energy around us?
- Planck’s Constant is very small. The Quanta are too small for every day notice, but to a very small atom they make a big difference

- In the photoelectric effect, electrons are ejected from the surface of a metal when light shines on it.
- Einstein realized that Planck’s idea of energy quanta could explain this.
- Said that Light consists of quanta of energy that behave like tiny particles, called PHOTONS

- Red light will not cause electrons to flow in a sheet of sodium metal, no matter how long or bright the source is. Violet light will cause electrons to flow. Violet light has a greater frequency, and a greater amount of energy per photon

- The frequency of light and the energy of the photon explains the effects of electromagnetic radiation.
- X-rays contain high amounts of energy because of their frequency, while radio waves have low frequency and low energy.

- Arthur Compton later demonstrated that photons can collide with electrons.
- Photons behave like a particle that always travels at the speed of light.
- E = mc2 =h